The present invention is directed to bicycles and, more particularly, to an internal bicycle hub transmission.
Internal hub transmissions generally comprise a hub axle fixed to a bicycle frame and a hub body rotatably mounted around the hub axle. A planetary gear mechanism is housed within the hub body so that rotational drive force of a drive member driven by the bicycle chain can be communicated to the hub body through various transmission paths. A clutch mechanism including a clutch member is provided for selecting the transmission path, wherein the clutch member may be controlled by axially moving it with a push rod. Such a hub transmission is disclosed in U.S. Pat. No. 5,928,103, wherein additional means are provided to facilitate actuation of the clutch member.
In this conventional hub transmission, the drive member always engages the clutch member regardless of the currently selected gear (e.g., high speed, medium speed or low speed). Thus, when backpedaling, the reverse rotation of the drive member is always accompanied by reverse rotation of the clutch member. Furthermore, when the hub transmission is in high speed, the clutch member and the planet gear carrier are coupled together, so they both rotate in the reverse direction during backpedaling. In any event, backpedaling is not smooth and requires more pedaling effort than desired.
The drive member disclosed in U.S. Pat. No. 5,928,103 is adapted to mount one chain sprocket for engaging the chain. Other hub transmissions have a drive member with an increased axial length so that multiple chain sprockets may be mounted to the drive member. However, when the axial extension of the hub increases to accommodate several sprockets on the outer periphery, additional mechanical loads arise in the drive member. For example, opposite ends of the hub axle are mounted to the bicycle frame, and the bicycle wheel is disposed between these two ends. Thus, the downward weight of the cyclist is supported at the ends of the hub axle while the bicycle wheel produces an upward counteracting force. This, in turn, causes a bending moment and a slight deflection to be applied to drive member. The pedaling force applied to the chain by the rider induces a torsional force in the drive member, thus causing further deflection. These deflections create additional friction and drag, decrease smoothness and increase the required pedaling effort.